[ms45xx] fix and improve ms45xx driver

- the behavior is now the same than before #2303: default pressure
  output is PSI, butterworth filter enabled by default
- add an auto_offset setting to zero the sensor before flight

conf/modules/airspeed_ms45xx_i2c.xml

@@ -24,6 +24,7 @@
     <dl_settings>
       <dl_settings NAME="MS45XX">
         <dl_setting min="0" max="1" step="1" values="FALSE|TRUE" var="ms45xx.sync_send" type="bool" shortname="sync_send" module="modules/sensors/airspeed_ms45xx_i2c" param="MS45XX_SYNC_SEND" persistent="true"/>
+        <dl_setting min="0" max="1" step="1" values="FALSE|TRUE" var="ms45xx.autoset_offset" type="bool" shortname="autoset offset" module="modules/sensors/airspeed_ms45xx_i2c" param="MS45XX_SYNC_SEND" persistent="true"/>
         <dl_setting min="0.9" max="1.2" step="0.01" var="ms45xx.pressure_scale" type="float" shortname="PressScale" module="modules/sensors/airspeed_ms45xx_i2c" param="MS45XX_PRESSURE_SCALE" persistent="true"/>
         <dl_setting min="0" max="1" step="1" values="FALSE|TRUE" var="ms45xx.pressure_type" type="bool" shortname="Type G" module="modules/sensors/airspeed_ms45xx_i2c" param="MS45XX_PRESSURE_TYPE" persistent="true"/>
         <dl_setting min="8300.0" max="8900.0" step="0.1" var="ms45xx.pressure_offset" type="float" shortname="PressOffset" module="modules/sensors/airspeed_ms45xx_i2c" param="MS45XX_PRESSURE_OFFSET" persistent="true"/>

sw/airborne/modules/sensors/airspeed_ms45xx_i2c.c

@@ -66,7 +66,7 @@ PRINT_CONFIG_MSG("USE_AIRSPEED_MS45XX set to TRUE since this is set USE_AIRSPEED
  *  if not defined to be MS45XX_PRESSURE_OUTPUT_TYPE_InH2O then PSI is used
  * */
 #ifndef MS45XX_PRESSURE_OUTPUT_TYPE_InH2O
-#define MS45XX_PRESSURE_OUTPUT_TYPE_InH2O 1
+#define MS45XX_PRESSURE_OUTPUT_TYPE_InH2O 0
 #endif
 
 /** MS45xx pressure range in PSI or InH2O
@@ -77,11 +77,18 @@ PRINT_CONFIG_MSG("USE_AIRSPEED_MS45XX set to TRUE since this is set USE_AIRSPEED
 #define MS45XX_PRESSURE_RANGE 1
 #endif
 
-/* Pressure Type 0 = Differential, 1 = Gauge , note there are theoretical more types than 2, e.g. Absolute not implemented */
+/** Pressure Type 0 = Differential, 1 = Gauge
+ * note there are theoretical more types than 2, e.g. Absolute not implemented */
 #ifndef MS45XX_PRESSURE_TYPE
 #define MS45XX_PRESSURE_TYPE 0
 #endif
 
+/** Use low pass filter on pressure values
+ */
+#ifndef USE_AIRSPEED_LOWPASS_FILTER
+#define USE_AIRSPEED_LOWPASS_FILTER TRUE
+#endif
+
 /** MS45xx output Type.
  * 0 = Output Type A with 10% to 90%
  * 1 = Output Type B with 5% to 95%
@@ -96,7 +103,7 @@ PRINT_CONFIG_MSG("USE_AIRSPEED_MS45XX set to TRUE since this is set USE_AIRSPEED
 /** Conversion factor from psi to Pa */
 #define PSI_TO_PA 6894.75729
 
-#ifdef MS45XX_PRESSURE_OUTPUT_TYPE_InH2O
+#if MS45XX_PRESSURE_OUTPUT_TYPE_InH2O
 #define OutputPressureToPa InH2O_TO_PA
 #else
 #define OutputPressureToPa PSI_TO_PA
@@ -131,6 +138,12 @@ PRINT_CONFIG_MSG("USE_AIRSPEED_MS45XX set to TRUE since this is set USE_AIRSPEED
 #endif
 #endif
 
+PRINT_CONFIG_VAR(MS45XX_OUTPUT_TYPE)
+PRINT_CONFIG_VAR(MS45XX_PRESSURE_TYPE)
+PRINT_CONFIG_VAR(MS45XX_PRESSURE_RANGE)
+PRINT_CONFIG_VAR(MS45XX_PRESSURE_SCALE)
+PRINT_CONFIG_VAR(MS45XX_PRESSURE_OFFSET)
+
 /** Send a AIRSPEED_MS45XX message with every new measurement.
  * Mainly for debugging, use with caution, sends message at ~100Hz.
  */
@@ -156,7 +169,9 @@ PRINT_CONFIG_MSG("USE_AIRSPEED_MS45XX set to TRUE since this is set USE_AIRSPEED
 
 struct AirspeedMs45xx ms45xx;
 static struct i2c_transaction ms45xx_trans;
+#ifdef USE_AIRSPEED_LOWPASS_FILTER
 static Butterworth2LowPass ms45xx_filter;
+#endif
 
 static void ms45xx_downlink(struct transport_tx *trans, struct link_device *dev)
 {
@@ -179,10 +194,10 @@ void ms45xx_i2c_init(void)
 
   ms45xx_trans.status = I2CTransDone;
   // setup low pass filter with time constant and 100Hz sampling freq
-  #ifdef USE_AIRSPEED_LOWPASS_FILTER
+#ifdef USE_AIRSPEED_LOWPASS_FILTER
   init_butterworth_2_low_pass(&ms45xx_filter, MS45XX_LOWPASS_TAU,
                               MS45XX_I2C_PERIODIC_PERIOD, 0);
-  #endif
+#endif
 
 #if PERIODIC_TELEMETRY
   register_periodic_telemetry(DefaultPeriodic, PPRZ_MSG_ID_AIRSPEED_MS45XX, ms45xx_downlink);
@@ -197,8 +212,13 @@ void ms45xx_i2c_periodic(void)
   }
 }
 
+#define AUTOSET_NB_MAX 20
+
 void ms45xx_i2c_event(void)
 {
+  static int autoset_nb = 0;
+  static float autoset_offset = 0.f;
+
   /* Check if transaction is succesfull */
   if (ms45xx_trans.status == I2CTransSuccess) {
 
@@ -218,11 +238,23 @@ void ms45xx_i2c_event(void)
        */
 
       float p_out = (p_raw * ms45xx.pressure_scale) - ms45xx.pressure_offset;
-      #ifdef USE_AIRSPEED_LOWPASS_FILTER
+#ifdef USE_AIRSPEED_LOWPASS_FILTER
       ms45xx.pressure = update_butterworth_2_low_pass(&ms45xx_filter, p_out);
-      #else
+#else
       ms45xx.pressure = p_out;
-      #endif
+#endif
+
+      if (ms45xx.autoset_offset) {
+        if (autoset_nb < AUTOSET_NB_MAX) {
+          autoset_offset += p_raw * ms45xx.pressure_scale;
+          autoset_nb++;
+        } else {
+          ms45xx.pressure_offset = autoset_offset / (float)autoset_nb;
+          autoset_offset = 0.f;
+          autoset_nb = 0;
+          ms45xx.autoset_offset = false;
+        }
+      }
 
       /* 11bit raw temperature, 5 LSB bits not used */
       uint16_t temp_raw = 0xFFE0 & (((uint16_t)(ms45xx_trans.buf[2]) << 8) |

sw/airborne/modules/sensors/airspeed_ms45xx_i2c.h

@@ -36,6 +36,7 @@ struct AirspeedMs45xx {
   float airspeed_scale;        ///< Quadratic scale factor to convert (differential) pressure to airspeed
   float pressure_scale;        ///< Scaling factor from raw measurement to Pascal
   float pressure_offset;       ///< Offset in Pascal
+  bool autoset_offset;         ///< Set offset value from current filtered value
   bool sync_send;              ///< Flag to enable sending every new measurement via telemetry for debugging purpose
 };